v0.8.0

• Float * Rational, Float / Rational, and Rational / Float now have correct overflow and underflow behavior; now all Float functions do, except for string conversion, which will be rewritten.
• The natural logarithm of 2 is now available as Float::log_2_prec and Float::log_2_prec_round.
• Floats now have a full complement of EqAbs implementations. Existing EqAbs and PartialOrdAbs implementations throughout Malachite have been cleaned up. Primitive unsigned integers no longer implement these traits, which is a breaking change. (If you were using these for some reason, just use normal comparison operators instead).
• Thanks to Will Youmans for implementing IsPower and ExpressAsPower for Naturals. I ported these implementations to u128 as well.